UNIVERSITY   OF  CALIFORNIA 

COLLEGE    OF  AGRICULTURE 

AGRICULTURAL    EXPERIMENT    STATION 

CIRCULAR  No.  255 
December,  1922 

LEGUMINOUS  PLANTS  AS  ORGANIC  FERTILIZERS  IN 
CALIFORNIA  AGRICULTURE 

By  P.  B.  KENNEDY 


Legume  Trial  Garden  at  Berkeley,  1922 


INTRODUCTION 

This  circular  is  intended  as  an  introduction  to  a  series  of  circulars 
dealing  with  leguminous  crops  suitable  for  growing  under  the  con- 
ditions which  prevail  in  California. 

The  arable  lands,  orchard  and  grain,  have  been  slowly  but  surely 
becoming  less  fertile  with  a  steady  decline  in  crop  yields.  This  ex- 
ploitation of  soil  fertility  by  the  removal  of  the  crop,  the  burning 
out  of  the  organic  matter,  and  the  leaching  out  of  the  nutritive  prop- 
erties of  the  soil  deserves  serious  consideration  from  the  urban  as 
well  as  the  rural  population  of  every  community. 


Z  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  change  from  horse  power  to  motor  power,  together  with  the 
low  rate  of  growth  of  the  animal  industries  as  compared  with  the 
plant  industries,  leaves  little  to  be  expected  from  animal  manures, 
the  demand  being  far  greater  than  the  supply.  Our  attention  there- 
fore turns  to  the  vegetable  manures  as  being  the  safest,  surest,  and 
most  economical  solution  of  the  soil  fertility  problem.  The  utilization 
of  legumes  as  green  manure  crops  will  go  far  toward  restoring  and 
maintaining  soil  fertility.  No  system  of  farming  should  be  con- 
sidered rational  that  does  not  include  a  liberal  use  of  legumes,  which 
add  to  the  nitrogen  content  of  the  soil  instead  of  depleting  it.  Nitro- 
gen is  one  of  the  most  essential  elements  for  plant  growth  as  well  as 
the  most  expensive  to  maintain.  It  is  readily  leached  out  by  rains 
and  irrigation  so  that  it  must  be  constantly  renewed.  It  is  therefore 
especially  necessary  to  consider  at  all  times  in  farming  opera- 
tions how  this  important  element  may  be  most  economically  in- 
troduced into  the  soil.  The  fact  that  it  is  possible  by  means  of  le- 
gumes to  utilize  the  atmospheric  nitrogen,  so  abundant  and  free  to 
all,  makes  the  importance  of  the  subject  apparent. 

The  Legume  Bacteria. — The  legume  organism,  to  which  this  fact 
is  due,  is  very  active  in  certain  stages  of  its  development,  and  gains 
entrance  to  the  root  mainly  through  the  tip  of  the  root  hairs.  This 
is  probably  accomplished  by  the  aid  of  an  enzyme  which  dissolves 
the  cell  wall.  Multiplication  by  division  from  one  to  thousands  takes 
place  in  a  short  time.  The  numerous  bacteria  produced  incite  the 
plant  cells  in  the  root  to  form  a  growth  which  we  term  a  nodule.  A 
specific  type  of  organism  and  nodule  occurs  in  each  group  of  related 
legumes.  Within  certain  limits  these  bacteria  are  interchangeable. 
To  illustrate:  the  bacteria  of  sweet  clover,  bitter  clover,  bur-clover, 
-and  alfalfa  are  interchangeable  for  purposes  of  inoculation,  so  that 
if  a  field  which  has  been  growing  a  good  crop  of  bur-clover  is  to  be 
planted  to  alfalfa  there  would  be  no  necessity  for  inoculating  the 
seed  or  soil  artificially.  Other  legumes  that  have  a  sympathetic 
relationship  with  regard  to  their  legume  organisms  are  peas,  len- 
tils, vetches,  horse  beans  and  sweet  peas,  while  soy  beans  are  not 
benefited  by  the  organisms  of  any  other  group.  The  true  clovers, 
red,  alsike,  crimson,  white  Dutch,  and  Egyptian  or  berseem,  form 
another  group.  Still  another  group  in  which  the  bacteria  are  inter- 
changeable comprises  cowpeas,  velvet  beans,  peanuts  and  Japan 
clover.  Lupines  which  occur  so  abundantly  in  California  are  probably 
of  no  value  for  inoculating  the  soil  with  bacteria  for  any  of  our 
common  garden,  field,  or  cover  crops.     So  that  much  depends  upon 


Circular  255]    leguminous  plants  as  organic  fertilizers  3 

whether  a  legume  of  any  kind  has  been  growing  in  the  soil,  and  if 
that  particular  legume  will  associate  from  an  inoculation  point  of  view 
with  the  one  we  wish  to  plant. 

Leguminous  Plants. — To  give  an  idea  of  the  number  and  varia- 
bility of  leguminous  plants  we  may  say  that  there  are  about  6500 
species  belonging  to  the  family,  or  10,000  or  more  kinds  if  we  include 
the  different  strains  of  garden  and  field  peas  and  beans.  They  are 
widely  distributed  in  all  countries,  but  most  abundantly  in  the 
tropics.  Many  of  them  are  well  known,  such  as  alfalfa,  sweet  clover, 
bitter  clover,  red,  crimson,  alsike,  and  white  Dutch  clover,  bur-clovers, 
lupines,  sweet  peas,  vetches,  velvet  beans,  soy  beans,  and  peanuts. 
Others  not  so  well  known  are  the  Spanish  clovers,  horse  beans,  fenu- 
greek, mung  beans,  jack  beans,  sword  beans,  lentils,  grass  peas,  gar- 
banzos,  kudzu,  carob  beans,  seradella,  sulla,  guar,  berseem,  Tangier 
pea,  Scotch  broom,  furze,  mesquite  beans,  Japan  clover,  sainfoin, 
sesbania,  sunn  hemp,  and  hyacinth  bean.  Numerous  additional  species 
occur  as  native  plants  furnishing  much  wild  forage  in  our  valleys  and 
mountains.  There  are  a  host  of  leguminous  trees,  shrubs,  herbs, 
and  climbing  plants  that  are  valuable  mainly  for  shade  and  orna- 
mental purposes. 

The  problem  then,  is  to  determine  which  of  these  legumes  will 
grow  satisfactorily  in  a  given  region.  The  purpose  for  which  the 
legume  is  to  be  grown,  whether  for  hay,  pasture,  soiling,  silage,  cover 
crop,  or  green  manure,  must  be  considered,  and  having  decided  this  a 
study  must  be  made  of  the  climate,  precipitation,  and  soil  conditions, 
and  whether  the  crop  is  to  be  grown  with  or  without  irrigation. 

CULTUEAL  EEQUIEEMENTS 

Nearly  all  legumes  require  for  their  best  growth  a  well-drained 
soil.  Some  of  them  respond  to  applications  of  lime  or  sulfur, 
or  both.  They  will  grow  on  a  great  many  types  of  soil,  from 
stiff  clays  to  light  sands,  but  prefer  good  loams.  Few  of  them  are 
tolerant  of  alkali  even  in  small  amounts. 

COVEE  CEOPS 

It  has  been  stated  again  and  again  that  our  California  soils  need 
humus  more  than  anything  else.  By  humus  is  meant  the  organic 
matter  in  the  soil  in  process  of  decomposition.  The  long  hot  summers 
have  a  tendency  to  burn  out  this  organic  matter,  bringing  about  a 
poor  physical  condition.  Hence,  the  advantage  of  a  crop  to  cover 
the  soil  during  the  hottest  part  of  the  summer  or,  what  we  term,  a 
cover  crop.    When  the  winter  or  summer  legume  is  plowed  under  it 


4  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

forms  humus  which  will  transform  stiff  soils  that  are  hard  to  work 
into  friable  loams.  If  the  soil  is  sandy  and  inclined  to  be  porous 
and  leachy  the  addition  of  humus  will  change  its  physical  condition 
so  that  it  will  be  more  retentive  of  moisture,  less  inclined  to  leach, 
and  less  liable  to  be  blown  about  by  the  wind.  Humus  also  affects 
the  temperature  of  a  soil  in  a  beneficial  manner  by  diminishing  ex- 
tremes, so  that  it  makes  a  soil  cooler  in  summer  and  warmer  in 
winter.  Very  few  soils  in  California  are  in  danger  of  having  such 
an  excess  of  humus  that  they  would  be  too  retentive  of  moisture,  thus 
excluding  the  air,  and  bringing  about  putrefaction  instead  of  the 
useful  decomposition  of  the  organic  matter.  The  plowing-under  of 
legumes  to  improve  the  physical  condition  of  the  soil  is  as  important 
as  the  contribution  of  plant  food  which  they  make.  One  of  the  most 
important  functions  of  humus  is  to  make  the  soil  habitable  for  the 
micro-organisms  or  bacterial  flora  which  play  such  a  large  part  in 
the  formation  of  plant  food.  The  mere  fact  of  mineral  nitrogen, 
phosphorus  and  potash  being  in  the  soil,  is  not  sufficient,  for  with- 
out humus  these  do  not  make  a  fit  habitat  for  the  growing  plant.  A 
soil  may  be  considered  good  from  an  agricultural  standpoint  if  it 
contains  from  one  to  two  per  cent  of  humus.  The  temperature  of  the 
soil  has  an  important  bearing  on  the  availability  of  the  plant  food. 
Nitrification  takes  place  to  a  slight  extent  at  40°  F.  and  increases 
up  to  99°  F.  Above  that  it  diminishes  again  and  stops  altogether 
at  130°  F.  It  is  necessary,  therefore,  not  only  to  plow  under  the 
legume,  but  to  have  the  proper  conditions  of  moisture  and  tempera- 
ture to  decompose  it  before  it  can  feed  the  crop. 

The  choice  of  a  green-manure  crop  should  be  based  on  the  avail- 
able water  supply,  both  for  the  growing  of  the  crop  and  for  its  de- 
composition when  turned  under.  Applications  of  "  strawy ' '  barn- 
yard manure  have  been  made  where  the  land  was  not  irrigated  that 
were  harmful  rather  than  beneficial,  as  the  material  did  not  decay 
but  left  air  spaces,  thus  causing  an  additional  loss  of  moisture  at  the 
most  critical  time. 

LEGUMES  AS  A   SOUECE   OF  NITEOGEN 

So  much  attention  has  been  drawn  to  the  nodules  on  the  roots  of 
legumes  as  " nitrogen  gatherers"  that  their  nitrogen  value  when  com- 
pared with  the  nitrogen  in  the  total  plant  has  been  over-rated.  It  is 
true  that  the  nodules  are  very  rich  in  nitrogen,  some  of  them  as  high 
as  7.25  per  cent,  and  that  it  is  probably  in  a  form  directly  available 
as  plant  food,  while  the  root  itself  has  only  one  to  three  per  cent  of 
nitrogen.    The  weight  of  the  nodules,  however,  is  but  a  small  fraction 


CIRCULAR  255]      LEGUMINOUS  PLANTS  AS  ORGANIC  FERTILIZERS  5 

of  the  total  root,  so  that  in  most  instances  the  roots  contain  less  nitro- 
gen than  the  tops.  Alfalfa  and  red  clover  have  their  nitrogen  more 
equally  divided  between  the  roots  and  the  tops.  The  former  because 
of  its  extensive  root  system  and  the  latter  because  of  its  numerous 
fine  roots  which  are  abundantly  noduled.  Analyses  reported  by  the 
Delaware  Agricultural  Experiment  Station,  Bulletin  No.  60,  1903, 
have  shown  58  per  cent  of  the  nitrogen  of  the  alfalfa  in  the  tops  and 
42  per  cent  in  the  roots  and  68  per  cent  in  the  tops  and  32  per  cent  in 
the  roots  of  red  clover.  On  the  other  hand,  vetch,  a  commonly  grown 
cover  crop  in  California  has  been  found  to  contain  89  per  cent  of  its 
nitrogen  in  the  tops  and  11  per  cent  in  the  roots,  soy  beans,  93  per 
cent  in  the  tops  and  7  per  cent  in  the  roots,  and  cow  peas,  84  per  cent 
in  the  tops  and  6  per  cent  in  the  roots. 

The  benefit  of  utilizing  both  the  tops  and  the  roots  of  a  legume 
as  green  manure  is  apparent.  Feeding  the  legume  as  hay  and  re- 
turning the  manure  to  the  land,  as  in  the  case  of  feeding  livestock, 
has  certain  advantages.  Organic  matter  or  humus  under  suitable 
conditions  is  attacked  by  micro-organisms  which  bring  about  de- 
composition and  during  the  process  carbonic  acid  and  other  acids 
are  formed.  These  acids  liberate  the  mineral  matter  in  the  soil  and 
make  it  available  as  plant  food.  Thus  three  important  elements, 
nitrogen,  potassium,  and  phosphorus,  are  made  available  for  the 
growth  of  the  plant  by  the  use  of  green  manure. 

TONNAGE  OF  VEGETABLE  MATTEE 

The  amount  of  green  vegetable  matter  produced  above  ground 
by  the  various  legumes  varies  from  ten  to  thirty  tons  per  acre.  A 
ton  of  green  legume  material  may  contain  from  ten  to  thirteen  pounds 
of  nitrogen,  so  the  amount  of  nitrogen  added  to  the  soil  may  be  from 
one  hundred  to  four  hundred  pounds,  according  to  the  legume,  and 
the  tonnage  of  humus  is  subject  to  a  similar  variation.  Taking  12 
cents  as  the  commercial  price  for  a  pound  of  nitrogen  and  the  growth 
from  the  Tangier  peas  as  twenty  tons  of  green  stuff  per  acre  we 
would  be  adding  to  the  soil  $24.00  worth  of  nitrogen  to  each  acre  by 
plowing  under  a  crop  of  such  peas.  There  is  no  cheaper  method 
of  applying  nitrogen  and  humus  to  the  soil  than  this.  The  cost  of  a 
ton  of  ordinary  barnyard  manure  as  bought  and  sold  is  many  times 
that  of  a  ton  of  green  manure  when  we  consider  the  expense  of 
getting  it  incorporated  with  the  soil.  There  is  the  added  expense 
of  hauling  and  distribution  on  the  land.  The  same  may  be  said  of 
chopped  alfalfa  hay.  Moreover,  there  is  no  certain  method  of  stand- 
ardizing the  value  of  these  products. 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION 


CONDITIONS  OF  SUCCESS 

The  benefit  therefore  of  a  good  stand  of  the  legume  is  evident. 
A  firm  rather  than  a  loose  seed  bed  is  essential.  To  plow  the  land 
and  sow  the  seed  before  the  soil  has  settled  is  one  of  the  most 
common  causes  of  failure.  Next  in  importance  is  the  quality  of 
the  seed.  If  the  seed  is  viable  and  has  been  certified,  one  can 
afford  to  pay  a  higher  price,  as  much  less  seed  per  acre  is  required. 
It  also  eliminates  any  doubt  as  to  whether  the  cause  of  failure  can 
be  attributed  to  the  quality  of  the  seed.  Certified  seed  does  not  con- 
tain noxious  weeds,  which  is  another  important  item. 

Frequently  there  is  a  soil,  especially  sandy  soil,  that  is  so  de- 
pleted of  plant  food  that  it  is  not  capable  of  producing  the  first 
green-manure  crop.  Under  these  circumstances  an  application  of 
superphosphate  will  give  the  legume  the  necessary  encouragement. 
Spots  in  the  field  that  have  been  scraped  or  are  known  to  be  non- 
productive should  receive  a  light  application  of  barnyard  manure. 

Seeding  should  be  done  early  in  September  or  October  for  winter- 
growing  crops  so  that  the  young  plants  can  take  advantage  of  the 
warm  weather  and  make  a  good  root  growth  before  cold  weather  sets 
in.  When  well  established  the  frost  may  check  them,  but  not  kill 
them,  while  if  small  and  recently  germinated  it  may  destroy  the 
small  tender  seedlings.  Sometimes  from  one  cause  or  another  a  good 
stand  of  a  legume  is  not  obtained  the  first  time.  There  are  in- 
stances where  the  first  season  produced  only  a  few  scattered  plants, 
while  a  trial  the  following  season  with-  the  same  legume  produced  a 
dense  stand.  The  reasons  have  not  always  been  apparent,  but  in- 
creased inoculation  may  have  something  to  do  with  it.  A  thin  stand 
the  first  time,  provided  the  plants  have  nodules,  will  provide  ample 
inoculation  of  the  soil  for  the  second  season's  crop. 

SELECTION  OF  A  LEGUME 

The  selection  of  the  legume  to  be  grown  will  depend  on  local  moist- 
ure, soil,  and  climatic  conditions.  In  the  northeastern  counties  where 
the  climate  will  not  permit  of  growing  a  crop  in  winter,  spring  sowing 
must  be  practiced.  Red  clover,  sweet  clover,  hubam  clover,  alsike 
clover,  alfalfa,  field  peas  and  hairy  vetch  will  probably  be  found  the 
most  satisfactory  for  this  purpose. 


CIRCULAR  255]      LEGUMINOUS  PLANTS  AS  ORGANIC  FERTILIZERS  7 

In  general,  coarse  heavy-stemmed  legumes  will  produce  the  most 
organic  matter  where  there  are  facilities  for  irrigation  to  supply 
ample  moisture  to  aid  in  the  decomposition  of  the  material  that 
is  turned  under.  Such  legumes  as  the  small-seeded  horse  bean,  the 
Tangier  pea,  cowpeas,  and  soy  beans  are  of  this  nature.  The  former 
are  winter-growing  and  the  two  latter  summer-growing  legumes. 
Legumes  producing  a  finer  leaf  and  stem  growth  than  these  are  the 
common,  hairy,  woolly-podded  and  purple  vetches  and  the  monanthos 
lentil  or  vetch.  These  should  be  utilized  in  sections  of  the  state 
that  have  to  depend  upon  the  natural  precipitation  for  the  moisture 
supply. 

The  following  lists  of  legumes  are  recommended  as  green  manure 

crops  for  California: 

Winter-growing  Sandy  Soil 

Hubam   Clover                                  .  Bitter  Clover 

Bitter  Clover  Hairy  Vetch 

Bur-clover  Bur-clover 

Garbanzos  (Cicer)  Lupines 

Small-seeded  Horse  Beans  Peanuts 

Tangier  Pea  Cowpeas 

Fenugreek  Soy  Beans 
Hairy  Vetch 

Purple  Vetch  Alkali  Tolerant 
Woolly-podded  Vetch 

Monanthos  Lentil  ?erS?^  C1°Ver 

Lupines  Sweet  Clover 

r  Hubam  Clover 

Summer-growing  Alfalfa 

_  Hairy  Vetch 

Cowpeas  Horse  Beans 

Velvet  Beans 

5?y  BeT?nS  Heavy  Soil 

Mung  Beans  J 

Tepary  Beans  Peas 

Berseem  Clover  Tangier  Pea 

Peanuts  Horse  Beans 

Alfalfa  Mung  Beans 

Sesbania  Sesbania 

Moth  Bean  Fenugreek 

Knowledge  of  legumes  has  increased  very  materially  in  the  last 
ten  years.  The  University  of  California  with  its  different  agencies 
has  been  alive  to  the  problem,  and  the  work  of  Webber  and  Mertz 
of  the  Citrus  Experiment  Station  at  Riverside  is  particularly  note- 
worthy. Trial  legume  gardens  are  supervised  by  the  writer  at  Berke- 
ley, the  Kearney  Experiment  Station,  Fresno,  and  the  Imperial 
Valley  Experiment  Station,  El  Centro.  From  these  it  is  determined 
what  varieties  seem  to  be  the  most  promising  and  they  are  grown  for 
further  experimentation.  The  following  counties  are  actively  coop- 
erating with  the  Agricultural  Extension  Service  of  the  University 


8  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

in  trials  and  demonstrations  with  legumes :  Fresno,  Glenn,  Humboldt, 
Imperial,  Kern,  Kings,  Los  Angeles,  Merced,  Napa,  Santa  Barbara, 
San  Benito,  Sonoma,  Stanislaus,  Sutter,  Tulare,  and  Yuba. 

Among  the  laymen  we  have  P.  A.  Ingvason  who  has  done  much 
to  introduce  and  make  available  a  number  of  important  new  legumes. 
A.  F.  Etters,  0.  E.  Lambert,  F.  P.  Bell,  C.  S.  Milliken  and  L.  A.  Clark 
are  others  whose  work  with  legumes  will  make  its  mark  on  the  in- 
creased fertility  and  production  of  California  soils. 

Some  of  the  newer  legumes  are  the  Tangier  pea,  the  monanthos 
vetch  or  lentil,  the  woolly-podded,  Hungarian,  and  bitter  vetches, 
sesbania,  mung  beans,  the  small-seeded  horse  bean,  and  the  moth 
bean.  These  have  proved  valuable  under  experimentation  and  will 
soon  be  known  and  recognized  as  commercial  legumes. 

Every  encouragement  should  be  given  growers  in  the  legume 
field  as  it  means  much  to  the  continued  prosperity  of  California 
agriculture. 


